1. Field of the Invention
The invention relates to crosslinkable organopolysiloxane-polyurea copolymers, to a process for preparing the crosslinkable organopolysiloxane-polyureacopolymers, and to their use, and also to crosslinkable compositions comprising the crosslinkable organopolysiloxane-polyurea copolymers, to the preparation of the crosslinkable compositions, to their vulcanization, and to the use of the vulcanizates.
2. Description of the Related Art
Organopolysiloxane-polyurea block copolymers are known and are prepared by copolymerizing diisocyanates and siloxanes terminated with aminoalkyl groups (Polymer, Vol. 25 (1984, p. 1800 f.).
The formation of hydrogen bonds between the urea groups allows these copolymers to be thermoplastic elastomers. Such copolymers are therefore plastic above the softening point, while below it they have elastic properties. Hence they can be used, for example, as hotmelt adhesives. A disadvantage of the use of such copolymers as hotmelt adhesives is, however, that the adhesive bond is reversible by an increase in temperature beyond the softening point. Moreover, moldings or adhesive bonds produced from such copolymers are subject to cold flow, as even below the softening point hydrogen bonds are able continually to separate and reattach, so that deformation and hence failure of the desired function are possibilities. Accordingly the field of use is limited to applications where no heightened temperatures and/or forces act on the thermoplastic elastomer.
One solution to the problem is to crosslink the individual polymer chains additionally with covalent bonds, i.e., thermally irreversible bonds. If, in production, the thermoplastic elastomers are crosslinked through the use, for example, of trifunctional units, then the processing properties (e.g., melt viscosity) may be adversely affected. Crosslinking after application is therefore more sensible.
EP 0 250 248 B1, EP 0 822 952 A1 and DE 101 13 980 A1 describe, for example, organopolysiloxane-polyurea block copolymers which have been provided with moisture-crosslinkable silyl end groups. This allows crosslinking by the end groups, after application in liquid melt form. The achievable crosslinking density is low, however, particularly in the case of long-chain block copolymers with a small end group concentration, but on the other hand a high degree of polymerization of the block copolymers is necessary for the development of the thermoplastic properties.